A good rule of thumb is that the softer it is the faster it can be cut.
You will be able to run a rod of teflon at speeds that are well abouve
the range of the average metal lathe. If you get worried about melting,
use coolant.
You are correct, aluminum is too soft to be a unicycle axle, unless you
dramatically increase the axle's diameter.
KH splines are machined directly from a sloid bar, no welds involved.
Unless you get a blem hub, there shouldn't be any welding anywhere on
the hub. It is done on a cnc mill (don't bother trying to buy one to do
this job custom on. The average cnc mill capable of this will cost
around $10 grand), but you can do it on a precise bridgeport with a good
rotary base. It will be extremely difficult. Not something to be
attempted for a beginner machinist. The hardest part of the KH axle will
be getting the chromoly heat treated. You will have to send it off, and
you could have troubles finding a place that will 1-off it.
A standard lathe isn't equipped to thread long sections on the inside of
a metal tube. You would need controlled powerfeed on the tailstock, and
that is rare on a normal lathe. If you are thinkiung of something
different, you would just use the tool rest and a self-ground bit to do
the cutting, but that wouldn't be very good for long tubes, due to
chatter. I reccomend just getting a good, long hand tap of the right
size. These can be fo\und up to a diameter of around 2".
Having seen your drawings for the coasting hub, I think you should think
about how you will get those keys to line up while riding quickly. You
will seriously risk mashing the edges of the keys when they interlock
while riding. Maybe you should taper them or use a friction clutch like
on a drum brake instead. What if you had a ring with a slightly tapered
cone? The cone would be very easy to cut on the lathe.
Teflon won't be ideal for instide the hub, unless it's just for sliding
lateral forces. It will not be good as a surface for high-rpm rotations.
The average spoke length for a 3-cross 20" wheel is between 180 and
240mm.
--
gerblefranklin - Trials Unicyclist
http://gallery.unicyclist.com/Trials-Muni
"Peace cannot be kept by force. It can only be achieved by
understanding."-Albert Einstein
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